The chemical and semi-conductor industries have long been faced with the demand for valving arrangements capable of withstanding contact with corrosive chemicals. These industries require components which can not only withstand exposure to corrosive liquids at significantly higher temperatures, but the valving arrangements must also be of larger size so as to have the capacity for permitting greater flow therethrough.
At the present time, most valve assemblies for use in these environments utilize valve components constructed of synthetic materials such as teflon. While the basic components are suitable for exposure to these environments, nevertheless the conventional weakness of these valve assemblies is the valve seat. These assemblies typically employ a valve seat formed by an elastomeric ring in order to obtain the desired sealing and sliding engagement between the valve seat and the movable valve member such as a ball. These elastomeric valve seat rings, however, tend to deteriorate when exposed to high temperature corrosive liquids, and hence the sealing characteristics of the valve deteriorate so as to require shutdown and repair.
Another problem encountered with valves of this type occurs in those use applications where the same system is used for controlling flow of different fluids at different times. For example, in systems employing a batch-type operation, one fluid may be pumped through the system for a selected period of time, with the system thereafter being flushed out, following which a different fluid will be pumped through the system. In such use environments, particularly when using fluids requiring careful isolation or separation such as dionized water or other pure fluids, it is extremely important that the valve be capable of handling these different fluids without causing cross-contamination. In valves which employ conventional elastomeric seat rings, however, it has been discovered that such cross-contamination is possible. These elastomeric seat rings have limited porosity, and some of the liquid becomes trapped in the pores of the seat rings, which trapped liquid cannot be readily cleansed. Hence, when the system is switched over for use with a different liquid, some of the trapped liquid gradually leaks into the pure liquid and causes undesired contamination thereof.
Accordingly, it is an object of the present invention to provide an improved valve assembly, specifically a ball valve assembly, which can successfully overcome or at least greatly minimize the problems associated with prior art devices as explained above.
More specifically, the improved valve assembly of the present invention employs valve seats which are constructed of teflon and form part of an end seal member, with the teflon valve seats being of a thin and hence deformable arrangement backed by an elastic loading ring which is isolated from the liquid. The teflon valve seat hence can readily withstand exposure to the high temperature corrosive liquids without undergoing deterioration, and at the same time the teflon valve seat is nonporous so as to prevent cross-contamination problems. Since the elastic loading ring which backs the teflon valve seat is isolated from the liquid, it is not subjected to deterioration or cross-contamination problems. This improved ball valve assembly hence is particularly suitable for use with extremely pure and/or high temperature corrosive liquids.
Another advantage of the improved ball valve assembly of this invention, as aforesaid, is the manner in which the valve ball is floatingly mounted between the opposed valve seats so that the ball automatically centers itself onto the opposed valve seats so as to ensure a proper sealing engagement therewith, irrespective of manufacturing or operational variations. This also permits the valve ball to continue to maintain a proper center and sealed seating engagement with the valve seats, even after repeated numbers of operations, since the centering characteristic of the valve ball and the resilient backing of the teflon valve seats wholly compensates for incidental wear which may occur through repeated use of the valve assembly.
The improved ball valve assembly of the present invention includes a housing having a flow passage therethrough, and a valve ball movably positioned centrally of this flow passage. The valve ball can be rotated through an angle of substantially 90.degree. between an open position wherein an opening through the valve ball is aligned with the passage, and a closed position wherein the valve ball opening extends transversely of the passage. The housing mounts a substantially identical end seal member within each end of the passage for cooperation with one side of the valve ball. The end seal member is of a sleevelike construction and is formed from a nonporous chemically-inert material such as teflon. The end seal member has a sleeve part which fits within the end of the passage and defines a port which opens toward the valve ball. The end seal member, on the axially inner end thereof, has an annular mounting part of a blocklike cross section, which part is clampingly held within the housing, such as between the center and end parts of the housing. The sleeve and mounting parts of the end seal member are axially joined together by an annular bridging portion which is of a thin and somewhat flexible wall. This bridging portion is surrounded by an annular groove which separates the sleeve and mounting parts. A rigid retainer ring is disposed within this annular groove adjacent the outer part thereof for creating a substantially rigid axial backing between the sleeve and mounting parts, and this retainer ring externally surrounds a resilient or elastic seat loading ring which is confined within the inner end of the annular groove. This seat loading ring acts against the thin wall of the annular bridging portion, the latter having a curved corner which defines an annular seat for engagement with the valve ball. The loading ring resiliently urges this annular seat outwardly for snug sliding but sealing engagement with the adjacent side of the valve wall.
In the improved ball valve assembly, as aforesaid, the ball has the capability of moving transversely relative to the longitudinal axis of the valve stem, and the ball and stem combination can itself move transversely relative to the flow passage, whereby the ball is floatably mounted solely by the opposed seats.
Other objects and purposes of the invention will be apparent to persons familiar with arrangements of this general type upon reading the following specification and inspecting the accompanying drawings.